A thyristor is typically a two- or three-terminal solid-state semiconductor device with four layers of alternating n- and p-type semiconductor material. It is a bistable switch (i.e., a rectifier) that conducts when its gate receives a current trigger, and continues to conduct as long as it is forward biased (i.e., as long as the voltage across the device is not reversed). A three-terminal thyristor controls the large current of its two terminals (i.e., the anode and the cathode) with a smaller current supplied to a control, or gate, terminal. A two-terminal thyristor is designed to switch on if the potential difference across the anode and cathode exceeds a breakdown voltage (i.e., the potential difference provides a switching overvoltage). Because thyristors can control a relatively large amount of power in a small device, they are frequently used in power-switching circuits to control electrical power.
A Shockley diode has a four-layer p-n-p-n structure and is essentially a thyristor without a gate terminal. A thyristor or Shockley diode structure can be switched to the on state by several different mechanisms. See, e.g., F. E. Gentry et al., Semiconductor Controlled Rectifiers, Englewood Cliffs, N.J.: Prentice-Hall (1964); S. M. Sze, Physics of Semiconductor Devices, New York: Wiley, pp. 319-340 (1969); W. Shockley, Electrons and Holes in Semiconductors, Princeton, N.J.: Van Nostrand, pp. 111-114 (1950); and J. J. Ebers, “Four Terminal p-n-p-n transistors,” Proc. IRE 40, 1361 (1952). The Shockley diode was originally used for low voltage and low current applications in telephone switching circuits. Thyristors can carry high currents but are not generally considered fast switching devices due to their turn on mechanism, i.e. plasma spreading from the gate region to modulate the conductivity of the base regions. As such, if a large current is supplied to a thyristor too quickly, i.e. a high di/dt, the device will fail due to filamentation and destruction of one or more p-n junctions within the device. The Shockley diode structure itself can be used as a closing switch in numerous applications if its hold-off voltage and cross-sectional area are set appropriately. In the late 1960's and early 1970's, Schoen developed a high-current and high-voltage Shockley diode structure for power modulator applications. See W. H. Schroen, “Characteristics of a High-Current, High-Voltage Shockley Diode,” IEEE Trans. Electron Devices, ED-17, No. 9, 694 (1970). Schroen's focus was on providing a two-terminal closing switch for high current and high voltage applications. As shown in FIG. 1, Schroen proposed a switch 10 that used Shockley diodes 13 connected serially to form a high voltage stack 12. A blocking diode 11 at the bottom (i.e., cathode terminal) of the high voltage stack 12 of Shockley diodes 13 was necessary for application of the switching overvoltage to the anode and cathode terminals of the stack. Unfortunately, Shockley diodes are no longer commercially available. In wide-spread use today is Shockley-like thyristor structure called a transient voltage suppressors (TVS).
Therefore, a need remains for a high-voltage, high-current, high di/dt solid-state closing switch and a method for triggering three-terminal thyristors for high di/dt applications.